Preliminary Study Of TCE Removal By GAC/ZVI And GAC/ZVI/Pd

Trichloroethylene (TCE) is the most common chlorinated aliphatic hydrocarbons (CAHs) in groundwater. Widely used as an organic solvent, TCE has contaminated groundwater and soil environments through leakage and accidental releases. The objectives of this research were to establish an effective method for preparing granular activated carbon (GAC) samples impregnated with nanoscale zero-valent iron (GAC/ZVI) and nanoscale ZVI with palladium (GAC/ZVI-Pd) to function as reactive activated carbon (RAC) for removing TCE from water and to conduct the preliminary study of TCE removal by RAC. The GAC/ZVI samples were prepared by first loading GAC with different amounts of Fe(NO3)3, then roasting the loaded GAC at 300℃for 4 hrs, and finally reducing the newly formed GAC/Fe2O3 in NaBH4 solution; the GAC/ZVI-Pd samples were obtained by depositing fixed amounts of Pd, from Pd(CH3CO2)2 in methanol, on GAC/ZVI. Norit HD 3000, with the richest mesopores, hightest BET surface and TCE adsorptive capacity among the three base GACs, was chosen as the source GAC for preparing the RAC samples with up to 32% of ZVI. SEM photomicrographs confirmed the presence of nanoscale ZVI particles (50-100 nm) on the RAC surface. The adsorptive capacity indicators and BET surface area of the RACs were lower than the source GAC due to the Fe impregnation. The imbedded amorphous ZVI nanoparticles were well-distributed in the base GAC. The batch experimental data show that RAC was capable of reducing the TCE concentration quickly and effectively and that the concentration profile was consistent with the pseudo first order reaction model. The RAC adsorbed and dechlorinated TCE simultaneously and that 14.5-30.4% of the adsorbed TCE was dechlorinated in 48h. During the initial period, RAC removed the TCE primarily by adsorption. Increasing the ZVI loading, although might resulted in more TCE reduction, was detrimental to the RAC's adsorptive capacity. The TCE removal capacities of RAC atr different DO levels were almost the same; however, exposure to high DO (6.9mg/L) for a long period, ZVI might be oxidized and thus reduced its reductive capability. The batch RAC treatment data of different contact time and initial TCE concentration have demonstrated the overall removal by concurrent adsorption and dechlorination of TCE.